Several drugs, particularly antipsychotics and certain steroids, are known to induce severe weight gain. A weight gain of about 7% over ideal body weight is considered a significant health risk due to the accompanying obesity that might lead to diabetes and cardiovascular diseases as well as a multitude of other obesity related diseases including cancer. With the average weight and BMI rapidly increasing over the whole world, the problem becomes even more severe.
The so-called atypical antipsychotic drugs are increasingly used to treat severe psychiatric diseases, among those, schizophrenia, schizotypal disorders, schizoaffective disorders, affective disorders, delusional disorders, and psychosis caused by use of psychoactive substances. Atypical antipsychotics include amisulpride, sulpiride, clozapine, risperidone, olanzapine, quetiapine, ziprasidone, and aripiprazole. Typical antipsychotics include chlorpromazine, perpherazine, thifluoperazine, thiothixene, haloperidol, and fluphenzine. Atypical antipsychotics are less likely to cause extrapyrimidal side effects than the typical antipsychotics. In addition, atypical antipsychotics work on the negative symptoms and cognitive disturbances as well, which the typical antipsychotics generally do not.
Among the side effects of the atypical antipsychotics is weight gain, which in some cases is very pronounced. Clozapine and olanzapine are, especially, known to cause severe weight gain. The weight gain is an important side effect since it lowers patient compliance. Furthermore, patients with weight gain are at increased risk to develop diabetes, and a weight gain in this population would probably lead to even more cases of diabetes compared with the background population. Also, the typical antipsychotics and other CNS-active drugs such as lithium, mirtazapine, tri- and tetracyclic antidepressants, and valproat can cause weight gain.
It is not known exactly what causes the weight gain, but increased appetite as well as decreased metabolic rate are believed to be involved. Currently only very few drugs are on the market for controlling appetite and none with the primary mechanism of increasing or maintaining metabolic rate. The one appetite reducing drug on the market, sibutramine, acts in the CNS by modulating the serotonin neurotransmitter levels, and is considered contraindicated in patients with current or previous psychiatric disease.
GLP-1 has been described as an incretin hormone with a large array of effects. GLP-1 was discovered in 1984 and found to be an important incretin [Nauck, M. A.; Kleine, N.; Orskov, C.; Holst, J. J.; Willms, B.; Creutzfeldt, W., Diabetologia 1993, 36, 741-744]. It is released from the L-cells in the intestine upon a meal and potently releases insulin from the beta-cells in the pancreas. Numerous effects other than just stimulation of insulin release have been ascribed to GLP-1. In the pancreas, GLP-1 not only releases insulin, it does so in a glucose-dependent manner, and it has a number of other functionally important effects: stimulation of insulin biosynthesis, restoration of glucose sensitivity to the islets, and, stimulation of increased expression of the glucose transporter GLUT-2 and glucokinase. GLP-1 also has a number of effects on regulation of beta-cell mass, stimulation of replication and growth of existing beta-cells, inhibition of apoptosis, and neogenesis of new beta-cells from duct precursor cells, which leads to reduced hepatic glucose output. In the gut, GLP-1 is a potent inhibitor of motility and gastric emptying and has also been shown to inhibit gastric acid secretion. The inhibition of gastric emptying leads to decreased food intake and reduced body weight [Flint, A.; Raben, A.; Astrup, A.; Holst, J. J., J Clin Inv 1998, 101, 515-520; Zander, M.; Madsbad, S.; Madsen, J. L.; Holst, J. J., Lancet 2002, 359, 824-830]. Thus, the current belief is that the GLP-1 agonists may be able to control the progression of the type 2 diabetes disease by not only controlling blood glucose, but also by a number of other effects. GLP-1 has also been proposed to have direct effects on glucose uptake in liver, muscle, and adipose tissue, but the quantitative significance of these effects has been questioned [Kieffer, T. J.; Habener, J. F., Endocrine Reviews 1999, 20, 876-913]. New publications even suggest that it does not stop here, there may be specific receptors in the heart which along with the benefits of reducing blood glucose may protect from cardiovascular complications, and that GLP-1 stimulates memory and learning capabilities. A comprehensive review exists on the glucagon-like peptides [Kieffer, T. J.; Habener, J. F., Endocrine Reviews 1999, 20, 876-9139.
A large number of articles have been published on the effects of GLP-1 on food intake. GLP-1 reduces food intake, both after central administration and after peripheral administration (Turton, Nature 196:379;69-72, Flint J Clin Inv 1998, 101, 515-520). Also, central administration of high doses of GLP-1 induces taste aversion (Tang-Christensen, Diabetes 1998:47:530-537). However, site directed micro injections of GLP-1 into the PVN induces pharmacologically specific inhibition of feeding without induction of taste aversive behaviour (McMahon, Wellman, Am.J.Phys 1998:274,R23-R29). In animals having their arcuate nucleus lesioned by neonatal monosodium glutamate treatment, central administration of GLP-1 has lost its anorectic potential but is still inducing taste aversion (Tang-Christensen, Diabetes 1998:47:530-537). Further support of dissociated specific satiety inducing central targets of GLP-1 and non-specific taste aversion inducing central targets come from lesion studies showing that PVN constitute a target where GLP-1 elicits satiety whereas the central amygdala and the parabrachial nuclei constitute areas involved in mediating GLP-1 induced taste aversion (van Dijk and Thiele, Neuropeptides 1999: 33, 406-414). Other studies have confirmed that there are diverse roles of GLP-1 receptors in the control of food intake and taste aversion (Kinzig, J Neuroscience 2002:22(23): 10470-10476). Also, chronic repetitive central administration of the GLP-1 antagonist, exendin-9-39, enhances food intake suggesting that an endogenous tone of satiety mediating GLP-1 exists in central pathways mediating body weight homeostasis (Meeran, Endocrinology 199:140:244-250). In a human study, continuous infusion of GLP-1 to type 2 diabetic patients gave rise to marked improvement of glycaemic control and caused moderate yet non-significant weight loss (Zander, Lancet 2002: 359, 824-830). The site of the anorectic action of peripherally administered GLP-1 is unknown but participation of both central and peripheral sites in GLP-1 are likely, because a recent study has shown that radio labelled GLP-1 readily gains access to the central nervous system (Hassan, Nucl Med Biol 1999:26:413-420). The nucleus of the solitary tract is situated adjacent to the blood brain barrier free area postrema, and other studies using radio-labelled neuropeptides have shown that peripheral administration of neuropeptides gain access both to the area postrema as well as the adjacent subpostreme regions including the dorsal vagal complex (Whitcomb Am J Phys1990: 259:G687-G691). Thus, it is likely that peripherally administered GLP-1 enters the nucleus of the solitary tract with resulting impact on ascending neurones involved in regulation of food intake. Interaction of GLP-1 with vagal afferents from the gastrointestional tract should also be considered as mediator of its anorectic actions because transection of the vagus nerve renders the stomach of anaesthetised pigs insensitive to the akinetic actions of intravenously administered GLP-1 (Wettergren, Am J Phys 1998:275:984-992). Probably both vagal afferents and GLP-1 receptors accessible from the periphery are responsible for the anorexia induced by GLP-1, because we have seen that bilateral subdiaphragmatic vagotomy on rats carrying the anorectic GLP-1 producing tumour has no impact on the development of anorexia (Jensen, JCI 1998: 101:503-510). Last, GLP-1 has been shown to inhibit intake of different kinds of food, both rich in fat and in carbohydrate (Bjenning, Diabetes Res and Clin Prac 2000:50(1):S386).
Despite this in-depth knowledge it has never been described that a GLP-1 agonist could be used to treat drug-induced obesity.